Device for coating a continuous web of material

ABSTRACT

Known devices for coating a continuous web of material ( 13 ) comprise a casting container ( 1 ) which consists of a casting surface ( 8 ) for the discharge of the coating material in a free failing curtain (C); at least one distribution chamber ( 2 ) which extends in a transversal manner in relation to the direction of circulation of the web of material and which comprises a supply line ( 10 ) for the coating material and an discharge slit ( 9 ) which discharges onto the casting surface ( 8 ), and two lateral guiding elements ( 7, 12 ) which extend in a downward direction for the edges of the curtain (C). According to the invention, the lateral guiding elements ( 7, 12 ) are curved on the upper end thereof corresponding to the course of the casting surface, ( 8 ) whereon ( 8 ) the lateral guiding elements are fixed in an adjustable transversal manner and the coating material supply line ( 10 ) leads into the valve chamber ( 2 ) in the central area of the casting container ( 1 ).

FIELD OF THE INVENTION

The present invention relates to an apparatus for coating a continuouslymoving web with a liquid hopper that has:

a flow face for forming the coating material into a freely fallingcurtain,

at least one distribution chamber extending transversely of theweb-travel direction with an input for the coating material and anoutput slot on the pour surface, and

two lateral downwardly extending guides for the edges of the curtain.

STATE OF THE ART

In order to coat a moving web, such as a paper or cardboard web or metalor plastic foil, so-called curtain coaters are known where the coatingmaterial (plastic dispersion, pigmented paint, etc.) issues from a slotnozzle as a free-falling curtain that impinges the web. If two or morelayers are to be applied simultaneously, a so-called slide hopper isused where the various coats are first layered on a flow face one abovethe other and then drop together as a free-falling curtain. in order toensure a stable coating width of the curtain, the two curtain edges areeach guided by a guide extending from the liquid hopper adjacent thecurtain. In the apparatus of this type described in U.S. Pat. No.4,135,477 the guides are parts of side plates of the hopper.

A curtain coater is known from WO 01/047643 that makes it possible tovary the coating width over a wide range. To this end transverselymovable splitter elements are provided on each side of theconstant-width dropping curtain to separate out a curtain region. Thesplit off coating material is conducted off. It must either beexpensively recirculated or it is lost.

OBJECT OF THE INVENTION

It is thus an object of the invention so to improve a coating apparatusof the described type that different coating widths can be set withouthaving to recirculate or dispose of the coating material.

This object is attained in that the lateral guides have upper endsshaped to conform to the flow face and are mounted to be transverselyadjustable on the flow face, and that the coating-material input openscentrally in the hopper into the distribution chamber.

The solution of the invention makes it possible to set the width of thecoating material on the flow face issuing from the outlet slot of thedistribution chamber and the width of the curtain to the desired coatingwidth. It is thus no longer necessary when reducing the coating width tosplit off parts of the curtain or take apart the nozzle.

Since at the ends of the guide elements near the web there are nosplitters, the known elements for uniform application with straight andsharp coating edges can be provided for the web, as described in WO02/081,103 (translator's note: U.S. patent application Ser. No.10/474,790 filed 3 Dec. 2003); for example a suction element to preventformation of an edge bead.

The dependent claims described preferred and particularly advantageousembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing serves for describing the invention with reference toseveral embodiments:

FIG. 1 is a section through a slide hopper with two distributionchambers for applying two coatings, one over the other;

FIG. 2 is an enlarged detail view at the overflow edge of theapplication surface;

FIG. 3 shows the edge of the slide hopper in a view taken against theweb-travel direction;

FIGS. 4 and 5 are perspective views of a slide hopper with fourdistribution chambers and a steplessly adjustable curtain width;

FIG. 6 shows an adjustable insert for limiting the chamber width.

EMBODIMENTS OF THE INVENTION

The coating apparatus shown in the drawing serves for example in themanufacture of self-sticking labels or hard-foil strips for applying adispersion-type adhesive and other layers to a support strip, forexample a paper strip or a plastic foil. Because of its advantages, itcan serve to apply other dispersions on webs of paper, metal, orplastic, for example to make packing material or ink-jet paper and tocoat paper or cardboard webs with flow dies or microcapsules, as well asother special applications.

The coating device is constructed as a slide hopper and has a modularlyconstructed liquid hopper 1 having at least one distribution chamber 2extending transversely of a web-travel direction. The liquid hopper 1according to FIG. 1 is comprised of three modules 3, 4, and 5 as shownin FIG. 1. The module 3 closest to the curtain is provided with anoverflow edge 6 and has on the opposite side a recess that forms a firstdistribution chamber 2. Directly upstream of the module 3 is a furthermodule 4 that on one side closes the distribution chamber 2 of themodule 3 and that on the opposite side is formed with a seconddistribution chamber 2. The module 5 on one side seals the seconddistribution chamber 2 of the module 5 and on the other side closes theliquid hopper 1.

The upper surface of the liquid hopper 1 is formed as a flow face 8inclined downward downstream and the various layers coming from thedistribution chambers 2 lay on it. To this end each distributionschamber 2 has a outlet slot 9 extending the full length of thedistribution chamber 2 and opening at the flow face 8. The coatingmaterials are fed into the respective distribution chambers 2 viarespective passages 10 that lie in central regions of the liquid hopper1 at a sufficient spacing from the seal plates that laterally close thedistribution chambers 2. They are connected at the lower side of theliquid hopper 1 to supply lines for the coating materials. The feedpassages 10 preferably end relative to the web width exactly in thecenter of the respective distribution chambers 2 so that the coatingmaterial is uniformly distributed in the distribution chambers 2regardless of the current coating width.

The liquid hopper 1 according to FIG. 1 has two distribution chambers 2for applying two layers, the liquid hopper 1 according to FIGS. 4 and 5has four distribution chambers 2 for applying four layers. The number ofdistribution chambers 2 is directly determined by the number of modules3, 4, and 5.

The sides of the liquid hopper 1 are each provided with downwardlyextending guides 7 and 12 for the respective curtain edge, each havingan upper end conforming to the curvature of the flow face 8. Each pairof guides 7 and 12 extends along the flow face 8 and past its end thendown parallel to the curtain C as shown in FIG. 4 to immediatelyadjacent a web 13 to be coated. The guides 7 and 12 can be shiftedtransversely and secured along the flow face 8, this transversepositioning being done either manually or automatically, e.g. via apneumatic, electric, or hydraulic linear actuator. The guides 7 and 12serve to prevent the surface tension of the coating liquid from formingthick beads at the edges of the freely dropping curtain C.

As described in WO 02/0811103 the bar-shaped guides 7 and 12 each have aflat inner face turned toward the curtain C. A wetting agent, forexample water or the actual curtain liquid, is sprayed on the inner faceof each guide 7 and 12 to hold the curtain on the guides 7 and 12. Thewetting agent is fed in through a passage 14 that opens slightly abovethe overflow edge 6 of the flow face 8 and that is connected as shown inFIG. 2 to a supply line 15. The lower end of each guide 12 is providedwith a suction element 16 whose face turned toward the curtain C isaligned with the inner face of the guide 12. The curtain edge flowswithout disturbance down along the guide 12 and the suction element 16to the web 13. A suction line is connected to the suction element 16from outside by a suction passage 17 opening at a suction slot 18. Thesuction slot 18 extends perpendicular to the curtain C and has a lengthparallel to the web-travel direction of between 0.5 mm and 15 mm,preferably 0.5 mm to 1 mm and is so positioned on the lower face of thesuction element 16 that it is spaced between 0.5 mm and 3 mm from theweb 13. To maintain this spacing, the suction passage is downwardlyclosed by a thin floor 19 slightly inclined to the web 13 and ending inthe suction slot 18 at a sharp edge. The aspiration of the thick edge ofthe coating material thus is effective horizontally. At the same timethe sharp edge ensures constant release of the coating material withoutthe so-called “tea-pot effect.” To prevent deposits from forming in thesuction slot 18, it is flushed with an appropriate rinse liquid, forexample water. To this end two flush lines 20 extend generally parallelto the suction line toward the suction slot 18. The rinse liquid iscarried off with the aspirated coating material via the suction line 17.

In order that the edge of the curtain C engaging the web 13 can belimitedly adjusted crosswise of the web-travel direction, the two guides12 are made at their lower portions defining the curtain C of alimitedly flexible and elastic material, preferably of spring steel, asshown in FIG. 3. To brace and position each guide 12, there is adownwardly extending brace bar 21 parallel to and offset outward fromthe guide 12. The brace bar 21 is in all cases more rigid than the guide12 and made, for example, of stainless steel and ends at a slightspacing short of the suction element 16. An adjustment screw 22 that canbe moved against the guide 12 is provided at the lower end region of thebrace bar 21. The screw 22 makes it possible to position the free end ofthe guide and the suction element 16 fixed to it limitedly transverselyof the web-travel direction in order to set the exact position of thesuction slot 18. In addition the screw 22 also allows the shape of theguide 12 to be varied within limits in order to optimize the guiding andadherence of the curtain edge.

The guides 7 and 12 with the elements fixed to them can be steplesslypositioned transversely along the flow face 8 as shown in FIG. 4. Thelower guide 12 is fixed to a cover plate 23. The edge of the cover plate23 turned toward the curtain also forms the upper guide 7. Brackets 24fixed to the cover plate 23 are mounted on a linear mount 25. The linearmounts 25 are in turn fixed on a support plate 26. The support plate 26can be slid manually or automatically along a straight guide 27. FIG. 5shows how the support plate 26 fits with the straight guide 27. FIG. 5also shows that a bent-out lower part of the plate 26 is fixed to afurther lateral support plate 28. Guide rods 29 on whose ends aresecured inserts are guided and fixed in the lateral support plate 28.The guide rods 29 extend into the distribution chambers and aresurrounded by radial seals in a seal plate 30.

The cover plate 23 is shifted downstream in the web-travel direction bythe linear mount 25 to adjust the thickness of the curtain C. This liftsthe cover plate 23 from its in-use position lying on the flow face 8. Itis also possible to pivot the cover plate 23 at its downstream edge sothat the cover plate 23 can be lifted off the slide face. Then, to setthe coating thickness the support plates 26 and 28 are movedperpendicular to the curtain C. This can be done manually by simplypushing or pulling the support plates 26 and 28 or can be done by meansof an unillustrated actuator. As the support plates 26 and 28 move theyslide in guides that are connected with the linear guide 27. At the sametime the guide rods 29 are shifted into or out of the seal plate 30.Inserts 31 are secured at the ends of the guide rods 29. The inserts 31are guided in the distribution chambers 2 and extend in the distributionchambers 2 to a position aligned with the inner edge of the cover platethat forms the upper guide 7. The inserts 31 are preferably made ofplastic and are provided with threaded inserts 32 in which therespective guide rods 29 are fixed. The inserts 31 limit the dimensionof the respective distribution chambers perpendicular (translator'snote: parallel) to the curtain and thus limits the width of the outletslot 9. After shifting the support plates 26 and 28 the cover plate 23is pulled back by means of the linear mount so that the cover plate 23lies directly on the flow face 8. The cover plate 23 serves at its edgeturned toward is the curtain again as the upper guide 7 and also as aseal for the outlet slot 9 above the insert 31 and outside the coatingwidth to seal the distribution chamber 2 that should not be filled withthe coating liquid.

The space outside the inserts 31 in the chambers 2, that is the regionremote from the curtain C, can if necessary be filled with a helperliquid. The nozzle can be used with or without this helper liquid in thespace outside the inserts 31. FIG. 5 shows an angle fitting 33 in theseal plate 30 for supplying the helper liquid to the distributionchambers, and this helper liquid can also be fed via the guide rods 29to the slide face of the inserts 31. The pressurized helper liquid inthe distribution chambers 2 outside the inserts 31 ensures that theinserts 31 do not get stuck or that the coating liquid for the curtain 3does not form deposits on the inserts 31 and wedge these inserts 31 inplace.

The helper liquid also ensures that adjustment of the width of theoutlet slot 9 is always possible. This makes it possible to steplesslyadjust the width of the outlet slot 9, and thus the width of the flowface 8, at any time with no disassembly. It is of course understood thatthe described width adjustment takes place on both sides of the nozzle,since both sides are spectrally identical.

The construction of the insert 31 is shown in FIG. 6. The insert 31 isformed for example of plastic and has preferably metallic threadedinserts 32. A thin base plate 34 is formed with a triangular-sectionbody 35 and a square-section body 36. The upper part of the base plate34 extends into the outlet slot 9 and the bodies 35 and 36 act as sealbodies in the distribution chambers 2. The guide rods 29 are threadedinto the inserts 32. The opposite face of the insert 31 delimits therespective distribution chamber 2 to the desired coating width of thecurtain. The insert 31 thus laterally closes the outlet slot 9 and thedistribution chamber 2 that are filled with the coating solution of thecurtain C, while the helper liquid behind the insert 31 prevents jammingof the insert 31.

The insert 31 is slid by two guide rods 29 that are anchored at one endin the insert 31 and at the other end in the respective lateral supportplate 28. The lateral support plates 28 flank the liquid hopper 1 andare each fixed to the respective support plate 26 so that they can bemoved jointly therewith transverse to the web-travel direction by adrive. The inserts 31 fixed to the guide roads 29 are so positioned thatthe width of the distribution chamber 2 is exactly the same as that ofthe flow face 8 and of the curtain C. The coating liquid only exits witha width that corresponds to the desired width of the coating. Thisensures that with any given coating width, no coating material is lostor needs to be recirculated.

In order to prevent the inserts 31 from sticking in the distributionchambers 2 during use so that they cannot be moved, they are wetted fromoutside with a rinse liquid, for example water or a solvent. To this endthe seal wall 30 is formed with passages that lead to the individualdistribution chambers 2 and that connect to the angle fittings 33 forthe rinse liquid. Preferably the inserts 31 fit with slight play in thedistribution chambers 2 so that some rinse liquid can get past andthrough the outlet slot 9 to the flow face, preferably the rinse liquidis fed under pressure into the distribution chambers. The rinse liquidcan also serves as helper liquid for the curtain edges to improveadherence to the guides 7. In some application the separate feed ofhelper liquid to the guide 7 can be eliminated. The rinse and helperliquids thus flow over the flow face 8 to the inner faces of the guides9 down to the lower guides 13 and ensure constant adherence of thecurtain edges.

FIGS. 1, 2, and 3 show the construction and mounting of the guide lower12 on the cover plate 23. The guide 12 is releasably mounted on thecover plate 23 by means of a knurled-head screw 34. The user thus canvery quickly disconnect the guide 12 from the cover plate 23. The guide12 on each side has two knurled-head screw 34, a seat plate 35, thebrace bar 21 with the adjustment screw 22, and the lower guide 12 andthe suction element 16 on the lower end of the guide 12. The two screws34 are held in seats 36 and engage with their threaded shafts into theseat plate 35 as shown in section in FIG. 2. The lower end of the seatplate 35 is fixed to the brace bar 21. The lower guide 12 on the otherhand is movable relative to the brace bar 21. The guide 12 can beadjusted transversely to the curtain C by means of the screw 22 througha limited angular travel shown at W in FIG. 3.

1-8. (canceled)
 9. An apparatus for applying a coating liquid to a webmoving in a travel direction, the apparatus comprising: a hopperdefining a distribution chamber extending transversely of the direction,a flow face extending generally in and transverse to the web-traveldirection, a slot extending between the chamber and the flow face andelongated transversely of the direction; means for supplying the coatingliquid to the chamber, thence through the slot to the flow face, andthence along the flow face and for dropping the liquid as a transverselyextending and downwardly flowing curtain from an edge of the flow faceonto the web; a pair of transversely spaced edge guides having upperguide elements having transversely confronting faces and fittablecomplementarily to the flow face, the upper guide elements lying in ause position substantially directly on the flow face to limit liquidflow to a region thereon defined between the transversely confrontingfaces that hence define the width of the curtain; and means fortransversely positioning the edge guides and thereby adjusting thecurtain width.
 10. The coating apparatus defined in claim 9 wherein eachedge guide further comprises a lower guide having an inner face alignedvertically with the face of the respective upper guide, the lower guidesbeing fixed to and transversely displaceable with the respective upperguides.
 11. The coating apparatus defined in claim 10, furthercomprising means at lower ends of the lower guides for aspirating thecoating liquid.
 12. The coating apparatus defined in claim 10, furthercomprising means for releasably securing the lower guides to therespective upper guides.
 13. The coating apparatus defined in claim 12wherein the releasable securing means includes finger-operable screws.14. The coating apparatus defined in claim 9 wherein the flow-face edgeis curved and fits with the upper guide element.
 15. The coatingapparatus defined in claim 9 wherein the flow face inclines downwardfrom the slot to the edge.
 16. The coating apparatus defined in claim 9wherein the hopper has a supply passage opening generally centrally intothe chamber, the supply means being connected via the passage to thechamber.
 17. The coating apparatus defined in claim 16, furthercomprising: a pair of transversely spaced inserts each substantiallyblocking the slot and the chamber; and means for transversely displacingthe inserts and thereby setting a transverse width of the chamber andslot.
 18. The coating apparatus defined in claim 17, further comprisingstructure linking the inserts to the respective guides for jointtransverse displacement therewith, the inserts having confronting innerfaces aligned vertically with the faces of the upper guides.
 19. Thecoating apparatus defined in claim 18 wherein the hopper includes endplates laterally flanking the inserts and the chambers, the structureincluding rods passing transversely through the end plates and havinginner ends fixed to the inserts.
 20. The coating apparatus defined inclaim 9, further comprising means for lifting the upper guides off theflow face during transverse displacement of the upper guides.